1. Field of the Invention
The present invention relates to an apparatus for, and a method of measuring total organic carbon (TOC) which is contained in sample water.
2. Description of the Background Art
In general, the content of total organic carbon which is contained in sample water is obtained by a method of independently measuring the contents of total carbon (TC) and inorganic carbon (IC) contained therein and calculating the difference therebetween as follows: EQU TOC=TC-IC
In this method, however, measurement errors caused in the measurement of the content of total carbon and the measurement of the content of inorganic carbon are included in the resulting TOC content, to problematically increase the total measurement error.
Another method of measuring the content of total organic carbon is called acid sparging treatment (or pretreatment). This method comprises the steps of acidifying sample water by adding inorganic acid thereto, sparging the acidified sample water with a gas containing no carbonic acid gas for removing inorganic carbon, and thereafter converting carbon, i.e., total organic carbon, which is exclusively left in the sample water, into carbonic acid gas and detecting the same, thereby measuring the content of total organic carbon. The acid sparging treatment is effectively applied to sample water which contains a considerably larger amount of inorganic carbon as compared with total organic carbon, such as that containing 100 p.p.m. of inorganic carbon and 10 p.p.m. of total organic carbon, for example, with a smaller measurement error as compared with the method of independently measuring the contents of total carbon and inorganic carbon.
With respect to still another method of measuring the content of total organic carbon, there has been proposed an apparatus for a method of introducing an acidified sample solution into a capillary which is made of a carbonic acid gas permeable material and decompressing the outer side thereof or introducing a carbonic acid gas absorbent solution such as a calcium hydroxide solution to the outer side thereof for outwardly removing inorganic carbon from the acidified sample solution through the carbonic acid gas permeable material, and thereafter measuring the content of carbon contained in the sample solution (refer to Japanese Patent Laying-Open Gazette No. 60-127460 (1985)).
In the acid sparging treatment, purgeable organic carbon (POC) which is contained in the sample is lost by volatilization during the sparging process for the acidified sample solution. If the sample contains chloroform, for example, about 100% thereof is lost. While purgeable organic carbon components include volatile and non-volatile materials, those having low boiling points and small water solubility, i.e., small affinity with water, are easily lost in general.
In the method of removing inorganic carbon contained in the acidified sample solution with the carbonic acid gas permeable material according to the aforementioned literature, a purge able organic carbon component which is contained in the sample solution is also lost through the carbonic acid gas permeable material since the decompressed gaseous phase which comes into contact with the acidified sample solution through the carbonic acid gas permeable material or the carbonic acid gas absorbent solution such as a calcium hydroxide solution contains no purgeable organic carbon component. In this case, the type of the lost purgeable organic carbon component and the degree of loss thereof are varied with the type and condition of the carbonic acid gas permeable material as employed, while a considerable amount of the purgeable organic carbon component is lost through a film of silicone rubber or polytetrafluoroethylene having continuous pores, which is employed in general.